Dtmf Detection

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    09-Jun-2015
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Transcript of Dtmf Detection

  • 1. Detection of DTMF signals Tomasz MarciniakE-mail: Tomasz.Marciniak @put.poznan.pl

2. OUTLINE

  • 1. DTMF signaling
  • 2. Calculation methods
  • 3. Comparison of arithmetic operations
  • 4. Improving of DTMF detection

3. DTMF signaling 4. DTMF signaling 5. DTMF signaling Example of DTMF application 6. DTMFgeneration Recommendation Q24 7. Calculation of DFT Direct method Multiplications: 2 N Additions:2( N -1) 8. Calculation of DFTFFT method

  • We can:
  • calculate two -point DFTs for two real signals using one -point FFT algorithm,
  • or
  • calculate one -point DFT (for one real signal decimated into two real signals) using one -point FFT algorithm.

9. Calculation of DFTFFT methods

  • Calculation process - four stages:
  • Pacing and bit-reversal of input
  • N -point complex FFT
  • Separation of odd and even parts
  • Generation of final output

10. Calculation of DFTFFT methods

  • Disadvantages of FFT algorithms:
  • computeall output samplesof the DFT ,
  • the spectrumdensity depends on thenumber of the input (output) samples,
  • the FFT needs anaccumulation of the allinput samples , before beginning of thetransformation ,
  • they requirememorizing many powersof thecomplex coefficient .

11. Calculation of DFTGoertzel algorithm 12. Goertzel algorithm 13. Comparison of real arithmetic operations FFT time divisionGoertzel algorithm DFT (direct) Number of additions Number of multiplications Method 14. Comparison When Goertzel is more effecitive? Goertzel FFT 15. Comparison When Goertzel is more effecitive? 16. Comparison When Goertzel is more effecitive? 17. Improving of DTMF detection Q:How we can reduce the number of DFT computations? A:By reductionof the numberNof the analyzed samples . 18. Improving of DTMF detection 19. Improving of DTMF detection

  • Typical solution :N =205
  • Proposed solution :
  • Calculation energy for80 N 85
  • and next correction

20. Improving of DTMF detection 21. Improving of DTMF detection Tests 22. Improving of DTMF detection Tests 23. Improving of DTMF detection Tests 0.56 Varying block 80 N 85 with correction 13.62 Varying block80 N 85 3.73 Constant blockN =80 1.30 Constant blockN =205 0.31 Constant blockN =1024 Difference between energy levels [%] Type of calculation